Spin lattice relaxation rates of tunnelling CD3 groups

Diezemann, Gregor; Sillescu, H.; Putten, D. van der

doi:10.1007/bf01309425

Cited by 24 publications

(24 citation statements)

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“…The sets of operators Vs, I z and I 2 on the one, and Vs, I z and Z on the other hand commute mutually, but 2 and I 2 do not commute. We may thus form linear combinations of the \m \m i7113) which are simulta neously eigenfunctions of Vs, I z and I 2 or of V% , I z, and Z. Diezemann [9], who treated spin relaxation in CD3 groups, preferred the first set. Using this set the largest block in the 7Y-matrix is a 7 x 7 block.…”

mentioning

confidence: 99%

Deuteron NMR of Methyl Groups in theTunneling Regime. A Single Crystal Study of Aspirin-CD₃

Detken

Focke

Zimmermann

et al. 1995

Zeitschrift Für Naturforschung A

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We dedicate this paper to Prof. Dr. Werner Müller-Warmuth on the occasion of his 65th birthday. Z. T. L. and U. H. owe much to his advice.We report the first single crystal deuteron NMR spectra of CD3 groups which display the socalled ±ß, ± (|a| ± ß) and ±(2|a| ± ß) lines characteristic of rotational tunneling in a sufficiently clear manner to allow a quantitative comparison with the respective theory developed in 1988 by the group of W. Müller-Warmuth. The molecular system we study is aspirin-CD3. We recorded spectra for differently oriented single crystals and measured spin-lattice relaxation times T\ in a wide temperature range. At 12.5 K we exploit the dependence of the ±(|a| ± ß) and ±(2|a| ± ß) lines on the orientation of the applied field Bo for determining the equilibrium orientation of the CD3 group in the crystal lattice. The spectra display features which allow, by comparison with simulated spectra, a measurement of the tunnel frequency ut. Its low temperature limit is (2.7 ± 0.1) MHz. It allows to infer the height V3 of the potential V(

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mentioning

confidence: 99%

Deuteron NMR of Methyl Groups in theTunneling Regime. A Single Crystal Study of Aspirin-CD₃

Detken

Focke

Zimmermann

et al. 1995

Zeitschrift Für Naturforschung A

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“…As in the high-temperature limit G,, (t) is identical with the classical correlation function exp (-Ft) the constants A~, 2 can be taken from the classical expression for the spin lattice relaxation rate of a randomly jumping methyl group [33,24]. The result (64) together with (60) is equivalent to that of Diezemann et al [26]. We feel, however, that our derivation is simpler, and, in any event, it reveals much clearer the relation between the deuteron spin lattice relaxation rate and the widths of the quasi-and inelastic lines in neutron scattering.…”

Section: -A~ G(~ol)+ Azg~(2~ol)mentioning

confidence: 59%

“…Diezemann et al have shown theoretically as well as experimentally that the analysis of spin-lattice relaxation times allows a determination of the librational energies of the methyl group [11,26]. These authors derived a theoretical expression for the relaxation time on the basis of the Hebel-Slichter equation.…”

Section: Introductionmentioning

confidence: 99%

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Quantum mechanical behaviour of deuterated methyl groups

Heuer

1992

Z. Physik B - Condensed Matter

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We discuss the temperature dependence of deuterium NMR spectra and spin-lattice relaxation rates i/7"1 of deuterated methyl groups. We restrict ourselves to the temperature range where it is sufficient to consider only the two lowest librational levels of the CD 3 group. Specifically we derive explicit expressions for 1/T~ and the width FNM R of the so-called tunneling resonances in the high-field NMR spectrum in the limit where the tunneling frequency A 0 is large compared to the quadrupole coupling constant of a methyl group. We demonstrate that the disappearance of the tunneling resonances at elevated temperatures follows the scenario of the NMR of nuclei which exchange classically between two inequivalent sites. We further show that the NMR linewidths and relaxation rates are strongly related to the widths of the quasielastic and inelastic lines in incoherent neutron spectra. It turns out that for NMR spectra the classical limit is usually reached at lower temperatures than for neutron spectra. All calculations are based on the projection operator formalism. tunneling frequencies larger than 10 .5 ~teV, the NMR spectrum of CD 3 groups allows an access of the tunneling process. This has been shown by Lalowicz et al. who calculated deuterium NMR single crystal and powder spectra of CD 3 groups as a function of the tunneling frequency for T= 0 [13]. Apart from the tunneling frequency A 0 the deuterium spectrum of CD 3 groups is governed by the nuclear quadrupole moment -electric field gradient interactions of the deuterons.

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“…The reason for this is very likely phonon-assisted tunneling through the barriers of the threefold methyl group potential. [23][24][25][26][27][28] As mentioned in the Introduction section, such tunneling has been observed in the neutron scattering data from CH 3 rotations for the ester group in PMMA. As we remarked then, there are two effects on the motion when replacing H by D. The hopping frequency shifts down by a factor of 2.…”

Section: Analysis Of the Dmr Line Shape Transitionmentioning

confidence: 99%

Tacticity effects on the barriers to rotation of the ester methyl group in poly (methyl methacrylate): A deuteron magnetic resonance study

Cereghetti

Kind

Higgins

2004

The Journal of Chemical Physics

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In isotactic poly͑methyl methacrylate͒ ͑PMMA͒, we investigate the dynamics of the ester methyl groups by means of deuteron magnetic resonance ͑DMR͒ in a deuterated sample. We find that the motion of the CD 3 -group affects the deuteron spin-lattice relaxation as well as the DMR line shape in a characteristic way. Quadrupolar order spin lattice relaxation measurements between T ϭ291 K and Tϭ70 K reveal a broad temperature dependent probability distribution of autocorrelation times c for the 2 /3 reorientation. This broad distribution corresponds to a temperature independent Gaussian distribution of activation energies (E a ) with variance E a ϭ13.8Ϯ0.5 meV ͑1.33 kJ/mol͒. The line shape transition between Tϭ70 K and Tϭ23 K is explained with the freezing in of the methyl group reorientation. By comparing our results in an 88% isotactic sample with results obtained from a 50% syndiotactic, 30% atactic, and 20% isotactic sample of a previous investigation, we demonstrate the higher local order of the 88% isotactic sample, which corresponds to a ratio of 1.6 in the relative width E a /E a of the E a distribution. We show that different stereospecific forms of PMMA can be easily distinguished by the characteristics of their line shape transition between Tϭ70 K and Tϭ23 K.

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Spin lattice relaxation rates of tunnelling CD3 groups

Cited by 24 publications

References 36 publications

Deuteron NMR of Methyl Groups in theTunneling Regime. A Single Crystal Study of Aspirin-CD₃

Deuteron NMR of Methyl Groups in theTunneling Regime. A Single Crystal Study of Aspirin-CD₃

Quantum mechanical behaviour of deuterated methyl groups

Tacticity effects on the barriers to rotation of the ester methyl group in poly (methyl methacrylate): A deuteron magnetic resonance study

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Spin lattice relaxation rates of tunnelling CD3 groups

Cited by 24 publications

References 36 publications

Deuteron NMR of Methyl Groups in theTunneling Regime. A Single Crystal Study of Aspirin-CD3

Deuteron NMR of Methyl Groups in theTunneling Regime. A Single Crystal Study of Aspirin-CD3

Quantum mechanical behaviour of deuterated methyl groups

Tacticity effects on the barriers to rotation of the ester methyl group in poly (methyl methacrylate): A deuteron magnetic resonance study

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Deuteron NMR of Methyl Groups in theTunneling Regime. A Single Crystal Study of Aspirin-CD₃

Deuteron NMR of Methyl Groups in theTunneling Regime. A Single Crystal Study of Aspirin-CD₃